Fig. 1. (Color online) (a) Schematic diagram of WSe₂/Bi₂O₂Se FET. (b) Optical micrograph of the WSe₂/Bi₂O₂Se FET.

Fig. 2. (Color online) (a) and (b) Output curves at gate voltages of 40 and 80 V with an inset of logarithmic coordinates. (c) and (d) Logarithmic diagram of the transfer curve at different bias voltage V_ds. (e) and (f) Current liner diagram in logarithmic coordinates, recorded by scanning gate voltage V_g.

Fig. 3. (Color online) (a) 3D-map of current, recorded by scanning gate voltage V_g and bias voltage V_ds. (b) The rectifying ratio of the forward current I_f to the reverse current I_r at the same gate voltage. (c) On/off ration of the Bi₂O₂Se/WSe₂ heterojunction.

Fig. 4. (Color online) (a) Kelvin Probe Force Microscopy (KPFM) image of the Bi₂O₂Se/WSe₂ FET, the inset shows KPFM line scan, denoted by a white dotted line in figure. (b) Ultraviolet photoelectron spectra of WSe₂ and Bi₂O₂Se. (c) Band diagrams of the Bi₂O₂Se/WSe₂ heterojunction.

Fig. 5. (Color online) Band diagrams of the junction with photoexcitation under the different V_ds and V_g, which reflected the charge transport process.

Fig. 6. (Color online) Photocurrent map of the Bi₂O₂Se/WSe₂ heterojunction field-effect transistor. (a) Bi₂O₂Se/WSe₂ heterojunction optical images, the white box indicates scanning area; (b) V_ds = 0 V, V_g = 0 V; (c) V_ds = 3 V, V_g = 40 V; (d) V_g = −3 V, V_ds = 40 V; (e) V_ds = 3 V, V_g = −40 V; (f) V_ds = −3 V, V_g = −40 V.

Fig. 7. (Color online) (a) Output curves of Bi₂O₂Se/WSe₂ heterojunctions under different light power irradiation. (b) Spectral response of the heterojunctions. (c) Response time of the device over one response cycle. (d) Composite comparison diagram of photoresponse performance among WSe₂-based photodetectors^{[11, 23−28]}.